Hot Water Supply System

ABSTRACT

A hot water supply system includes a first heat pump, a second heat pump, and a hot water storage tank. The first heat pump heats water stored in the hot water storage tank to make hot water. The second heat pump heats water supplied to the hot water storage tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry of PCT Application No. PCT/JP2020/024797, filed on Jun. 24, 2020, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hot water supply system.

BACKGROUND

Since the 1990s, a natural refrigerant heat pump hot water supply system “EcoCute (R)” has been used as a hot water supply system for an all-electric house. This is a hot water supply system in which hot water at about 90° C. is obtained using a heat pump that uses atmospheric heat as a heat source and carbon dioxide as a refrigerant. A carbon dioxide refrigerant (R744) is considered to be suitable for heat transfer under a large temperature difference. However, use of the carbon dioxide refrigerants especially in air-conditioning systems has not been widespread from the viewpoint of energy consumption efficiency or the like.

Under such circumstances, a hybrid type hot water supply system “ECO ONE” that concurrently uses electricity and gas is becoming widespread. This is a system having a configuration in which low-temperature heating is performed with a heat pump such that a temperature of water becomes about 50° C., and an energy-saving high-efficiency hot water supply device “ECO-JOZU (R)” is installed in the subsequent stage to compensate for an insufficient temperature and amount of hot water during hot water supply. It is reported that this system has achieved 156% hot-water-supply primary energy efficiency (Non-Patent Literature 1).

On the other hand, widespread use of an instantaneous water heater using 200-V commercial power has been also observed (Non-Patent Literature 2). In order to simplify a hot water supply system and reduce its initial installation cost, it may be effective, in some respects, to install such an electric heater type water heater in the subsequent stage of the natural refrigerant heat pump hot water supply system described above, in place of the energy-saving high-efficiency hot water supply device, to compensate for an insufficient temperature and amount of hot water during use of hot water. However, compared with efficiency of the energy-saving high-efficiency hot water supply device that is 95%, efficiency of the electric heater type water heater is estimated to be about 40% at best. Thus, from the viewpoint of energy efficiency, this is considered to be an apparent setback.

For industrial use, there is a product such as a circular-heating heat pump that achieves a high temperature (output temperature: up to 90° C.) (Non-Patent Literature 3). This product employs a cascade refrigerating cycle system, and obtains high-temperature water by heating water in a two-stage refrigerating cycle where a cascade heat exchanger is interposed between a heat source unit (a refrigerant R410A is used) and a supply unit (a refrigerant R134a is used).

CITATION LIST Non-Patent Literatures

-   Non-Patent Literature 1: Rinnai Corporation, “Gyokai Saiko no Kyuto     Ichiji Enerugi Koritsu 156% o Jitsugen Haiburiddo Kyuto, Dambo     Shisutemu ECO ONE (in Japanese) (Industry-Leading 156%     Hot-Water-Supply Primary Energy Efficiency Achieved, Hybrid Hot     Water Supply and Heating System ECO ONE)”, ALIANEWS, vol. 156, pp.     64-67, 2017. -   Non-Patent Literature 2: Nippon Kenso Kogyo Co., Ltd., “Eemax     Emakkusu Denshi Shunkan Yuwakashiki (in Japanese) (Eemax, Electronic     Instantaneous Water Heater)”, [retrieved on Jun. 22, 2020], Internet     <http://www.eemax.jp/prod_eemax.html>. -   Non-Patent Literature 3: Naoki Imato et al., “CAONS™ 140 Air-Source     Circular-Heating Heat Pump with Maximum Output Water Temperature of     90° C.”, Toshiba Review, Vol. 68, No. 7, pp. 52-55, 2013.

SUMMARY Technical Problem

However, in view of circumstances such as global warming, efficiency is expected to be further increased.

Embodiments of the present invention have been made to solve the above problem, and it is an object of embodiments of the present invention to further increase efficiency of a hot water supply system.

Means for Solving the Problem

A hot water supply system according to embodiments of the present invention includes: a first heat pump having a cycle in which a first refrigerant is caused to become high in temperature and pressure by a first compressor, then is forwarded to a first heat exchanger, and is expanded after becoming a low temperature and high pressure state through the first heat exchanger, the first heat pump being configured to heat water stored in a hot water storage tank to make hot water; and a second heat pump having a cycle in which a second refrigerant is caused to become high in temperature and pressure by a second compressor, then is forwarded to a second heat exchanger, and is expanded after becoming a low temperature and high pressure state through the second heat exchanger, the second heat pump being configured to heat water supplied to the hot water storage tank.

Effect of Embodiments of the Invention

As described above, according to embodiments of the present invention, the water, supplied to the hot water storage tank in which the stored water is heated by the first heat pump, is heated by the second heat pump. Thus, efficiency of the hot water supply system can be further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating a configuration of a hot water supply system according to an embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Hereinafter, a hot water supply system according to an embodiment of the present invention will be described with reference to FIG. 1 . The hot water supply system includes a first heat pump 101, a second heat pump 102, and a hot water storage tank 103. A water supply supplied to the hot water supply system is branched into a first pipe 122 and a second pipe 123 at a branch valve 121. Water carried through the first pipe 122 is supplied to the hot water storage tank 103. Further, hot water stored in the hot water storage tank 103 is carried to, for example, a mixing faucet 125 through a third pipe 124. Water carried through the second pipe 123 is mixed with hot water carried through the third pipe 124 at the mixing faucet 125, and is supplied to a use point 126 such as a bathtub or a shower.

The first heat pump 101 heats water stored in the hot water storage tank 103 to make hot water. The first heat pump 101 has a cycle in which a first refrigerant is caused to become high in temperature and pressure by a first compressor (not illustrated), then is forwarded to a first heat exchanger 104, and is expanded after becoming a low temperature and high pressure state through the first heat exchanger 104. The first heat pump 101 uses atmospheric heat absorbed in a fourth heat exchanger 105 as a heat source. The water stored in the hot water storage tank 103 is heated by exchanging heat between the water and the first refrigerant, in the first heat exchanger 104. For example, in the first heat exchanger 104, heat is exchanged between the first refrigerant at 50° C. and the water stored in the hot water storage tank 103. The first refrigerant may be, for example, a natural refrigerant such as carbon dioxide (R744). Alternatively, the first refrigerant may be difluoromethane (R32). The first heat pump 101 using difluoromethane is generally used for a household air-conditioning system, and has undergone advanced technological development.

The second heat pump 102 heats water supplied to the hot water storage tank 103. The second heat pump 102 has a cycle in which a second refrigerant is caused to become high in temperature and pressure by a second compressor (not illustrated), then is forwarded to a second heat exchanger 106, and is expanded after becoming a low temperature and high pressure state through the second heat exchanger 106. The water carried through the first pipe 122 is heated by exchanging heat between the water and the second refrigerant, in the second heat exchanger 106. For example, in the second heat exchanger 106, heat is exchanged between the second refrigerant at 90° C. and the tap water at 15° C. carried through the first pipe 122. The second refrigerant may be, for example, 1,1,1,2-tetrafluoroethane (R134a). Alternatively, the second refrigerant may be an azeotropic mixture (R410A) of difluoromethane and pentafluoroethane.

In this example, the second heat pump 102 uses a third heat exchanger 107 as a heat source. The third heat exchanger 107 exchanges heat between the first refrigerant that has been caused to become high in temperature and pressure by the first compressor of the first heat pump 101 and is forwarded to the second heat exchanger 106, and the second refrigerant. Alternatively, the second heat pump 102 may use atmospheric air as a heat source.

It is also possible to use carbon dioxide as the second refrigerant used in the second heat pump 102. However, in this case, it is necessary to further increase refrigerant circulation capacity of the second heat pump 102. The specific heat of carbon dioxide is 837 J/kg°C, while the specific heat of water is 4,182 J/kg°C. For example, when a temperature of tap water is 15° C. and is raised to 52.5° C., and when carbon dioxide serving as the refrigerant has a temperature of 90° C. and is cooled to 52.5° C. by heat exchange with the tap water in the second heat exchanger 106, a difference due to the temperature change is 37.5° C. When an assumption is made that amounts of heat mcΔT exchanged in the second heat exchanger 106 are equal, the specific heat of carbon dioxide is about one-fifth of the specific heat of water, and thus it is necessary to set the refrigerant circulation capacity of the second heat pump 102 five times the amount of the heat-exchanged water (the amount of water supply).

According to the above embodiment, as a result of using the hot water stored in the hot water storage tank 103, significant reduction in the temperature of the hot water stored in the hot water storage tank 103 is suppressed because the temperature of the tap water supplied to the hot water storage tank 103 is raised to a higher temperature in advance. Therefore, by continuing steady operation of the first heat pump 101, it is possible to constantly store, in the hot water storage tank 103, just a designed amount of hot water having a temperature constantly maintained at a set temperature.

For example, during the time between 15:00 and 19:00, the temperature of the water in the hot water storage tank 103 is raised to 50° C. by the operation of the first heat pump 101, and then, for example, the hot water at 50° C. is supplied from the hot water storage tank 103 to fill the bathtub with the hot water. For example, mixture with tap water is made at the mixing faucet 125, the temperature is thus adjusted, and then supply to the use point 126 is made. Further, to the hot water storage tank 103, tap water is supplied through the first pipe 122 after being heated through the second heat pump 102 (the second heat exchanger 106). Thus, the hot water storage tank 103 is resupplied with an insufficient amount of water. For example, the supply to the use point 126 is started after waiting for an outlet temperature of the second heat pump 102 to reach 50° C. In this manner, a load on the first heat pump 101 can be reduced without significantly reducing the temperature of the hot water in the hot water storage tank 103. The same applies to operations such as during bathing or during use of the shower as well as when the bathtub is filled with hot water. It should be noted that an instantaneous water heater using 200-V commercial power may be provided immediately before the use point 126.

As described above, according to embodiments of the present invention, the water, supplied to the hot water storage tank in which the stored water is heated by the first heat pump, is heated by the second heat pump. Thus, efficiency of the hot water supply system can be further increased. According to embodiments of the present invention, a heat pump for an air-conditioning system used in a general household can be used. Thus, advanced technologies refined through the development of these technologies can be used. Therefore, the system can be excellent in energy use efficiency.

It should be noted that the present invention is not limited to the embodiment described above, and it is apparent that various modifications and combinations can be made by those having ordinary knowledge in the art within the technical scope of the present invention.

REFERENCE SIGNS LIST

-   101 First heat pump -   102 Second heat pump -   103 Hot water storage tank -   104 First heat exchanger -   105 Fourth heat exchanger -   106 Second heat exchanger -   107 Third heat exchanger -   121 Branch valve -   122 First pipe -   123 Second pipe -   124 Third pipe -   125 Mixing faucet -   126 Use point. 

1-3. (canceled)
 4. A hot water supply system comprising: a first heat pump having a cycle in which a first refrigerant is configured to become higher in temperature and pressure by a first compressor, then is forwarded to a first heat exchanger, and is expanded after becoming a low temperature and high pressure state through the first heat exchanger, the first heat pump being configured to heat water stored in a hot water storage tank to make hot water; and a second heat pump having a cycle in which a second refrigerant is configured to become high in temperature and pressure by a second compressor, then is forwarded to a second heat exchanger, and is expanded after becoming a low temperature and high pressure state through the second heat exchanger, the second heat pump being configured to heat water supplied to the hot water storage tank.
 5. The hot water supply system according to claim 4, further comprising a third heat exchanger configured to exchange heat between the first refrigerant that has been caused to become high in temperature and pressure by the first compressor and is forwarded to the second heat exchanger, and the second refrigerant, wherein the second heat pump is configured to use the third heat exchanger as a heat source.
 6. The hot water supply system according to claim 4, wherein the second heat pump is configured to use atmospheric air as a heat source.
 7. A hot water supply system operation method comprising: performing, by a first heat pump, a cycle in which a first refrigerant becomes higher in temperature and pressure by a first compressor, then is forwarded to a first heat exchanger, and is expanded after becoming a low temperature and high pressure state through the first heat exchanger, the first heat pump being configured to heat water stored in a hot water storage tank to make hot water; and performing, by a second heat pump, a cycle in which a second refrigerant becomes high in temperature and pressure by a second compressor, then is forwarded to a second heat exchanger, and is expanded after becoming a low temperature and high pressure state through the second heat exchanger, the second heat pump being configured to heat water supplied to the hot water storage tank.
 8. The hot water supply system operation method according to claim 7, further comprising exchanging, by a third heat exchanger, heat between the first refrigerant that has been caused to become high in temperature and pressure by the first compressor and is forwarded to the second heat exchanger, and the second refrigerant, wherein the second heat pump uses the third heat exchanger as a heat source.
 9. The hot water supply system operation method according to claim 7, wherein the second heat pump uses atmospheric air as a heat source.
 10. A hot water supply system comprising: a first heat pump configured to heat water stored in a hot water storage tank, the first heat pump being further configured to perform a first cycle comprising: causing a first refrigerant to become higher in temperature and pressure by a first compressor; after causing the first refrigerant to become higher in temperature and pressure, forwarding the first refrigerant to a first heat exchanger; expanding, the first refrigerant, after causing the first refrigerant to become lower in temperature while in a high pressure state by the first heat exchanger; a second heat pump configured to heat water supplied to the hot water storage tank, the second heat pump being further configured to perform a second cycle comprising: causing a second refrigerant to become higher in temperature and pressure by a second compressor; after causing the second refrigerant to become higher in temperature and pressure, forwarding the second refrigerant to a second heat exchanger; expanding, the second refrigerant, after causing the second refrigerant to become lower in temperature while in a high pressure state by the second heat exchanger; and a third heat exchanger configured to exchange heat between the first refrigerant and the second refrigerant.
 11. The hot water supply system according to claim 10, wherein the third heat exchanger is configured to exchange heat between the first refrigerant and the second refrigerant after the first refrigerant has been caused to become high in temperature and pressure.
 12. The hot water supply system according to claim 10, wherein the third heat exchanger is configured to exchange heat between the first refrigerant and the second refrigerant after the first refrigerant has been caused to become high in temperature and pressure by forwarding the first refrigerant to the second heat exchanger.
 13. The hot water supply system according to claim 10, wherein the second heat pump is configured to use the third heat exchanger as a heat source.
 14. The hot water supply system according to claim 10, wherein the second heat pump is configured to use atmospheric air as a heat source. 